Synchronizing system for electrical musical instruments



April 3, 1956 o. SALA 2,740,892

SYNCHRONIZING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENTS Filed July 22, 1952 3 Sheets-Sheet l Fig- 1 i xx xxxxk f P s7 K 14v INVENTOR. 0AM

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Aida 1 4 0? April 3, 1956 o. sALA 2,740,892

SYNCHRONIZING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENTS Filed July 22, 1952 3 Sheets-Sheet 2 IN VEN TOR.

April 3, 1956 o. SALA 2,740,892

SYNCHRONIZING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENTS Filed July 22, 1952 3 Sheets-Sheet 3 INVENTOR. 04/ 04 BY ma /(M United States Patent G SYN CHRONIZING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENTS Oskar Sala, Berlin-Charlottenburg, Germany Application July 22, 1952, Serial No. 308,152 Claims priority, application Germany February 14, 1952 11 Claims. (Cl. 250-36) This invention generally relates to electrical musical instruments, and it relates particularly to a synchronizing arrangement for an electrical musical instrument of the type wherein grid-controlled gas discharge tubes are utilized for developing electrical oscillations having a continuously variable frequency.

The pitch of the tone of a musical instrument of the type to which the present invention relates is determined by the frequency of a saw-tooth voltage wave developed by a gas discharge tube or thyratron. The frequency of this voltage wave, in turn, is determined by the grid bias voltage of the thyratron. This grid bias voltage may be controlled by the player of the musical instrument by actuating a frequency-determining element such as a variable resistor functioning as a keyboard or manual.

The synchronizing arrangement or system serves the purpose of deriving simultaneously several tones or electrical frequencies having a subharmonic relationship. These subharmonic tones or frequencies are synchronized by a given or predetermined tone and are also developed by relaxation oscillators including gas discharge tubes. The subharmonic relationships must be maintained constant when the frequency of the given or predetermined tone is varied within a large frequency range. Ratios between the predetermined tone and the subharmonic tone of the order to l to must be obtainable. It is necessary to adjust or vary easily the desired ratios and to change them readily at will.

it is accordingly an object of the present invention to provide an electric network or system suitable for an electrical musical instrument by means of which two tones having a predetermined subharmonic relationship may be developed simultaneously.

A further object of the invention is to provide an electric system of the character defined where the pitch of the predetermined tone may be varied at will within wide limits without changing the predetermined subharmonic relation with the other tone or tones which are produced simultaneously with the predetermined tone.

An electrical system in accordance with the present invention includes a relaxation oscillator or generator for developing a saw-tooth voltage wave corresponding to the predetermined tone. Only the frequency of the wave developed by the relaxation generator serving as a synchronizing generatoris variable by varying the negative grid bias voltage by means of a frequency-determining element. Another relaxation generator is synchronized by the first generator and develops the subharmonic frequency or tone and is biased by a fixed negative grid bias voltage. The voltage wave developed by the synchronizing generator has a variable frequency and is fed to the grid of the synchronized generator by way of a grid-controlled high-vacuum tube which reverses the phase of the wave. The control grid of the vacuum tube is also coupled to the frequency determining element and hence its grid voltage is also varied or modified by the frequency-determining element or manual. This phase reversing vacuum tube is operated along the lower curved portion of its grid voltageanode current characteristic. Consequently, a voltage wave is developed at the grid of the synchronized relaxation generator, which has an amplitude that increases with frequency and which causes the synchronized generator to be locked-in in a very stable manner up to a very high subharmonic ratio and over a wide frequency range of the synchronizing generator.

The invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a circuit diagram of a synchronizing system embodying the present invention;

Fig. la is a circuit diagram of a portion of the system of Fig. 1 modified in accordance with the invention;

Fig. 2 is a graph illustrating Wave shapes derived from the circuit of Fig. 1; and

Figs. 3 to 6 are circuit diagrams of further embodiments of the invention.

Referring now to the drawings wherein the same elements are designated by the same reference characters and particularly to Fig. 1, there is shown a system for developing two saw-tooth waves having a predetermined subharmonic relationship. The system of Fig. l in cludes a relaxation generator 1 for developing a sawtooth voltage wave which synchronizes another relaxation generator 2!); hence, generator 29 is synchronized by generator 1. The saw-tooth waves are developed in a manner well known by the anode resistors 5 or 19 and by the capacitors 6 or 21, respectively. Generators 1 and 20 are gas tubes or thyratrons. in the rid circuit of generator 1 there is connected a frequency-determining element which may consist of a variable resistor 4 consisting of a stretched resistance wire. The two terminals of resistor 4 are secured to an insulator 4 so that one terminal of the resistor 4 is floating. A grounded metallic rod or plate 4" is disposed below the resistance wire 4 so that any desired portion of the resistance wire 4 may be connected between the control grid of tube 1 and ground through resistor 3 by touching a desired point of the wire 4 to the grounded plate 4". A negative grid bias voltage is applied to the grid of tube 1 from a negative source through potentiometer resistors 9 and 8, the latter being grounded. A variable point of resistor 8 is connected through a tap and variable resistor 2 to the control grid of tube 1. Resistor 3 and that portion of resistor 4 connected between ground and resistor 3 form a shunt circuit or bleeder which determines the grid bias voltage. The control grid of the synchronized generator 20 is supplied with a predetermined negative bias voltage through the resistors 16, 17

and 18 which is adjustable by the tap on resistor 17 and which must remain constant during synchronizing of the generator.

The synchronizing saw-tooth wave developed by generator 1 is fed to the control grid of the vacuum tube 12 through a de-coupling network including capacitor 10 and resistor 11. The control grid of the vacuum tube 12 is further coupled with the grid of the synchronizing generator 1 through resistor 13.

The capacitor 7 Connected between the control grid of thyratron 1 and ground serves for equalizing or leveling sudden jumps of the direct current grid voltage which may occur at resistor 4 during the step-wise variation of the resistance connected in the grid circuit. Furthermore, capacitor 7 suppresses the grid pulses of the generator 1 which may occur in the grid circuit when the tube fires. Preferably, the filament of the gas tube 1 is heated with direct current, to improve the stability of the circuit, while the filaments of tubes 12 and 20 may be fed with alternating current.

The synchronizing saw-tooth wave developed in the anode circuit of the vacuum tube 12 has its phase reversed and at the same time its amplitude is modulated in accordance with the frequency of the synchronizing wave, as will be more fully explained hereinafter. This is due to the fact that the operating point of the phase reversing tube 12 is shifted into the lower curved portion of its grid voltage-anode current characteristic. The synchronizing saw-tooth wave derived from the phase reversing tube 12 is impressed on the grid of the synchronized relaxation generator 20 by means of direct current of the blocking and coupling capacitor 15. The various subharmonic relationships between the frequencies of the waves are developed by generators 1 and 2t), adjusted by means of the variable anode resistor 19.

The operation of the circuit of Fig. 1 will now be explained by reference to Fig. 2. The graphs :1, b, c are obtained from an oscilloscope and illustrate saw-tooth waves of different frequencies of the .synchronizing generator 1 as impressed on the grid of the phase reversing tube 12. The particular frequencies F shown at a, 2F shown at b and 4F shown at have been selected from a continuously variable sequence of saw-tooth wave frequencies. The amplitude of the saw-tooth wave decreases, as is well known, with its frequency. The oscillographs d, e, 1, illustrating waves of frequencies which correspond respectively to the same frequencies F, 2P, 4P of the synchronizing saw-tooth wave are taken from the grid of the synchronized relaxation generator 20. The phase reversing tube reverses the direction of the voltage jumps P1 in curve a to P3 in curve d, and therefore, the jumps P are in the same direction as the pulses P2 of the synchronized generator shown at d. This eir'ect is believed to have an important stabilizing influence on the synchronizing arrangement.

Furthermore, the phase reversing tube 12 causes the amplitude of the synchronizing saw-tooth wave to increase with frequency at the grid of the synchronized generator 20. This is achieved due to the fact that a negative bias voltage is applied to the grid of the phase reversing tube 12 which is developed by the variable resistor 4; this bias voltage decreases with increasing frequency. When the operating point of the phase reversing tube 12 is in the region of the lower bend of the grid voltage-anode current characteristic, changes of the grid bias voltage caused by the resistor 4 cause a large change of the slope of the characteristic of the phase reversing tube 12. In this manner the slope of the characteristic of the phase reversing tube 12 can be increased with increasing frequency to such an extent that the decrease of the amplitude of the saw-tooth wave with frequency at the grid of the phase reversing tube 12, shown at a, I], c, is transformed into an increase of the amplitude of the waves d, e, f with frequency in the anode circuit of the phase reversing tube 12.

As soon as this over-compensated state is achieved it is possible to obtain an optimum synchronized lock-in condition by a fine adjustment of the anode resistor 14, grid resistor 17 and coupling resistor 13. This optimum lock-in condition extends over the entire control range provided by the resistor 4 and may amount to a maximum of three and one half octaves and is independent of the order number of the manual up to divisional ratios of 1 to 16.

The result of the synchronization proceses, that is, the synchronized wave is illustrated in Fig. 2 at g, h, i as obtained from the coupling network 22, 23. While the frequency ratios correspond to those of the curves a to c and d to f, the actual values of the frequencies are divided by seven in this case. Although the relaxation generator 26 has only one firing voltage which is adjusted once and for all it is still possible to force synchronization of the generator, that is to lock-in the generator within a continuous frequency range in the required subharmonic relationship because the missing portion of the predetermined firing voltage is supplied by the synchronizing wave, the amplitude of which increases with frequency.

With the circuit of Fig. 1 it has been possible to force subharmonic relationships up to about 1 to 20 over almost the entire range of the manual. In this connection the following interesting and important phenomenon has been established.

Every subharmonic relation of the synchronized re laxation generator which is smaller than the maximum obtainable divisional ratio can only be adjusted by varying the resistance of resistor 19 or the capacitance of capacitor 21; in that case the stability as well as the range of the relative frequency change which may be effected by the manual increases with decreasing divisional ratio 5.

When the thus obtained values of the resistance of resistor 19 and the capacitance of capacitor 21 are determined for the different subharmonic divisional ratios and when these fixed values are changed in accordance with Fig. In by stepping or sequence switches 36 or 37, it is found that these values do not vary during adjustment of the synchronized generator after it has been connected in circuit, as well as when the thyratron of the synchronized generator or the vacuum tube of the phase reversing tube are replaced. In all these cases, all that is necessary is to readjust the largest divisional ratio of the stepping switch 36 or 37 by means of the resistors 13, 14 and 17 when the tubes are replaced or to readjust the resistors 14 and 17 for a further fine adjustment which may be necessary after the circuit is connected again to obtain the desired tone range. After such adjustment the smaller values of the divisional or subharmonic ratios are also exactly correct and correspond to the desired and required tone range. In case several relaxation generators have to be synchronized simultaneously, it is possible to utilize for all the synchronized generators the same fixed values of the resistors 19 and of the capacitors 21 connected in a circuit which is otherwise the same. This exact determination of these fixed values needs only be effected for a single relaxation generator. These values may then be utilized, without further adjustment, for the remaining synchronized generators.

This type of adjustment provides a considerable simplification for the player. For example, if four synchronized relaxation generators are controlled by one synchronizing generator, each synchronized generator being adjustable by means of a stepping switch for a divisional ratio of between 1 to 2 and l to 16, the player is enabled to adjust completely and accurately these sixty selectively adjustable subharmonic ratios by a simple checking and readjustment, if necessary, of the four lowest subharmonic ratios (in the present case a ratio of 1 to 16) of each synchronized relaxation generator without the necessity to adjust or check the remaining fifty six values.

The circuit of Fig. 1 may be modified in various ways to provide synchronization of a plurality of synchronized generators. Some embodiments of such circuits will now be discussed by way of example. Fig. 3 is a circuit diagram for providing synchronization of a plurality of generators in parallel. The synchronizing saw-tooth wave derived from the phase reversing tube 12 is impressed on several synchronized relaxation generators 20, 20 and so on by way of decoupling tubes 25, 25' and so on, which latter serve the purpose to prevent feedback or reaction of the grid pulses between the various synchronized generators. The elements 24 to 29, 24 to 29' and so on should be selected and chosen in such a manner that an undistorted transfer of the synchronizing saw-tooth wave takes place. The decoupling tubes operate in the normal range of the characteristic in the conventional manner of a triode circuit' By means of resistors 19, 19 and so on various subharmonic intervals may be adjusted independently from each other.

Figs. 4 and 5 are circuit diagrams of systems for effecting synchronization of the synchronized generator in parallel or in series. The synchronized generators 20, 20 and so on are each coupled to a phase reversing tube 12, 12' and so on, the grids of which are coupled by separate resistors 13, 13' and so on with the grid of the synchronizing generator 1. The grids of the phase reversing tubes 12, 12 are supplied with the synchronizing saw-tooth wave by means of individual coupling networks 10, 11, 10', 11 and so on.

In accordance with Fig. 4 the saw-tooth wave of the relaxation generator 1 is applied by means of each coupling network 10, 11, 10', 11' and so on to each phase reversing tube 12, 12' and so on and is utilized as synchronizing wave and is impressed on the synchronized generators 2-9, 20 and so on to provide synchronization in parallel.

In accordance with Fig. there is utilized not only the saw-tooth wave of the relaxation generator 1 as a synchronizing wave but each synchronized saw-tooth wave of different frequency is used to synchronize, in turn, a further relaxation generator; thus a series synchronization system is obtained. By means of the coupling networks 31, 31; 22, 23; 22, 23 and so on the various saw-tooth waves may be derived either individually or simultaneously and may be rendered audible, for example, by means of elements which determine the timbre and of the amplifiers. Of course there is no free choice of the subharmonic frequencies for this series synchronization system so that the required equipment for numerous desired subharmonie frequencies may become too great. Therefore, it is of considerable practical importance that a stable synchronization is possible even for large subharmonic intervals because with such a system a relatively small expenditure of relaxation generators and coupling tubes provides very different and numerous combinations. In this connection it is very important that the subharmonic frequencies may be changed by means of a single knob or by unicontrol means.

In order to explain the possibilities which may be obtained with the synchronizing arrangement of the invention an interesting modification of the circuits described so far will now be explained in connection with Fig. 6. This system makes it possible to derive very peculiar wave forms which produce quite surprising sounds. As shown in Fig. 6 several synchronizing saw-tooth waves of different frequencies are impressed on a synchronized relaxation generator 32 by means of a phase reversing tube 35. These waves may be developed either by any of the previously described circuits or in any other known manner. These waves are impressed on tube 35 by means of coupling networks 33, 34; 33, 34' and so on. By way of example these synchronizing saw-tooth waves of different frequencies may be obtained from the relaxation generators 2t 20' of Figs. 3 to 5. If these waves with frequencies having harmonic relationship between each other are impressed simultaneously on the phase reversing tube 35, the non-linear operation of the tube 35 causes the development of difference or beat frequency waves of very large amplitudes, which of course, must bear a harmonic relationship to the impressed saw-tooth waves. These differences of the heat frequency waves are also developed as component of the synchronized saw-tooth wave derived from the generator 32 so that a subjective sound is produced which may roughly be compared to that of an organ mixture. The lowest fundamental tone is heard predominantly and besides the frequencies of the saw-tooth waves developed by the generators 20, 20' and so on as well as further, weaker harmonic components which produce a many-sided timbre. It is very remarkable that even in this multiple synchronization system the lock-in range remains invariably the same even if the impressed synchronized saw-tooth waves of the generators 29, 20' and so on have high subharmonic ratios with respect to the applied synchronizing saw-tooth wave. By means of adjustable coupling resistors 34, 34' and so on the mixing ratios of the audible timbre may be further controlled in many ways.

Since certain changes may be made in the above described arrangement and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A synchronized arrangement for electrical musical instruments comprising a first and at least one further relaxation generator, each including a grid-controlled gas discharge tube, said first generator developing a synchronizing saw-tooth wave, said further generator being synchronized by said synchronizing wave, means for impressing a predetermined negative bias voltage on the grid of said first geenrator, means including a frequencydetermining resistor connected to the grid of said first generator and operable to vary and to decrease said bias voltage with increasing frequency of said synchronizing wave, a phase reversing vacuum tube having a grid and a plate, means for impressing said synchronizing wave on the grid of said tube, a first connection between said frequency-determining resistor and said grid of said tube, said vacuum tube having a grid voltage-plate current characteristic characterized by a slope decreasing with increasing negative grid voltage, the direct current voltage of said plate being so arranged that the operating point of said tube is within the range of change of slope of said characteristic, whereby the negative grid voltage of said tube will decrease with an increase in frequency of said synchronizing wave of said first generator, and simultaneously the slope of said characteristic will increase and the amplitude of the synchronizing wave will increase on said plate, and a second connection between said plate and the grid of said further generator.

2. An arrangement as defined in claim 1 wherein a further variable resistor is included in said first connection between said frequency determining resistor and said grid of said tube.

3. An arrangement as defined in claim 2 wherein the gas discharge tube of said further generator includes an anode, and wherein a plurality of anode resistors is provided which are selectively connectible to the anode circuit of said further generator.

4. An arrangement as defined in claim 2 wherein the gas discharge tube of said further generator includes an anode and a cathode, and wherein a plurality of discharge capacitors is provided which are selectively connectible across said anode and cathode.

5. An arrangement as defined in claimZ wherein a plurality of further generators is provided, each being coupled to said vacuum tube by an individual decoupling tube, the grids of said decoupling tubes being coupled to said vacuum tube by individual coupling capacitors.

6. An arrangement as defined in claim 2 wherein a plurality of further generators and a plurality of phase reversing vacuum tubes is provided, each further generator being coupled to one of said vacuum tubes, the control grids of said vacuum tubes being coupled to said frequency-determining resistor by an individual further resistor.

7. An arrangement as defined in claim 6 wherein individual coupling elements are provided for coupling the control grids of each of said vacuum tubes to said first generator, thereby to impress said synchronizing wave on each of said vacuum tubes.

8. An arrangement as defined in claim 2 wherein a plurality of further generators is provided and a plurality of phase reversing vacuum tubes, each of said further generators being coupled to a preceding further generator through one of said vacuum tubes, whereby each of said further generators is synchronized by the preceding further generator.

9. An arrangement as defined in claim 2 wherein two further generators are provided and a further phase reversing vacuum tube, said further tube being coupled between said further generators connected in cascade, whereby the first one of said further generators synchronizes the other one of said further generators.

10. A synchronizing arrangement for electrical musical instruments comprising a plurality of relaxation generators, each developing a saw-tooth wave, said waves having frequencies harmonically related to each other, means for synchronizing said relaxation generators, a further synchronized relaxation generator, and a comrnon phase reversing vacuum tube coupling said plurality of generators to said further generator for simultaneously synchronizing said further generator by means of said waves.

11. An arrangement as defined in claim 10 wherein a coupling network including a variable resistor is provided for coupling each of said plurality of generators to said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,100,702 Schlesinger Nov. 30, 1937 2,355,287 Firestone Aug. 8, 1944 2,414,479 Miller Jan. 21, 1947 2,428,617 Dickinson Oct. 7, 1947 

